Scanning electron microscopic observations of treated and untreated wood residues of poplar and eucalyptus were carried out. We hoped to evaluate the different methods of treatment and study the effect that different conditions such as temperature, time, pressure and chemicals have on the physical modification of the wood residues. It was observed that wood samples which had been treated by continuous acid hydrolysis in a Cascade reactor at temperatures below 243C and discharge pressure below 4000 psi had little effect on the wood structure. At a moderate discharge pressure (2975 to 2500 psi), the degree of wood disruption increased with the increase in reactor temperature; thus more of the wood tissue was reduced to wood fibers and fiber bundles at 223C than at 208C. Although wood samples retained in the ractor for shorter times than 100 sec showed insignificant morphological changes, longer retention times may increase the outflow of lignin from the cell wall layers. Tetrahydrofluran was shown to remove the lignin deposits in the treated wood. Wood samples discharged from the reactor and subsequently washed with tetrahydrofluran showed clean fiber surfaces and separation of the fibers as fault lines developed among the fiber bundles. The wood samples of E. saliqua were more resistant to pretreament as compared to the samples from poplar wood. The process of liquefaction was shown to effectively alter the wood structure of poplar. The poplar wood chips which were treated at 320C for 5min followed by discharging at 520 psi contained shattered tissue fragments and associated spheres. Cellulose microfibrils however were not found in these treated wood samples.
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